System and method of rapid, comfortable parameter switching in spinal cord stimulation

ABSTRACT

A system and method for rapidly switching stimulation parameters of a Spinal Cord Stimulation (SCS) system increases the number of stimulation parameter sets that may be tested during a fitting procedure, or alternatively, reduces the time required for the fitting procedure. The switching method comprises selecting a new stimulation parameter set, and setting the initial stimulation levels to levels at or just below an estimated perception threshold of the patient. The estimated perception level is based on previous stimulation results. The stimulation level is then increased to determine a minimum stimulation level for effective stimulation, and/or an optimal stimulation level, and/or a maximum stimulation level, based on patient perception.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/829,742, filed Jul. 27, 2007(now U.S. Pat. No. 7,571,001), which is acontinuation of U.S. application Ser. No. 10/212,585, filed Aug. 5, 2002(now U.S. Pat. No. 7,263,402), which claims benefit of priority fromU.S. Application Ser. No. 60/311,856, filed Aug. 13, 2001. Thedisclosures of these applications are expressly incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to Spinal Cord Stimulation (SCS) systemsand more particularly to a system and method for rapidly switchingbetween SCS system stimulation parameter sets. An SCS system treatschronic pain by providing electrical stimulation pulses through theelectrodes of an electrode array, which electrode array is placedepidurally next to a patient's spinal cord. The stimulation parameterset specifies both the characteristics of the stimulation pulsesprovided through the electrode array, and the electrodes used to providethe stimulation pulses. An effective stimulation parameter set for aspecific patient may be determined from the response of the patient tovarious stimulation parameters sets. However, there may be a very largenumber of stimulation parameter sets, and evaluating all possible setsis very time consuming, and may be impractical.

Spinal cord stimulation is a well accepted clinical method for reducingpain in certain populations of patients. An SCS system typicallyincludes an Implantable Pulse Generator (IPG), electrodes, electrodelead, electrode lead extension, and at least one stimulation parameterset. The electrodes are implanted along the dura of the spinal cord, andthe IPG generates electrical pulses which are delivered, through theelectrodes, to the fibers of the spinal cord, according to thestimulation parameter set in use. Individual electrode contacts (the“electrodes”) are arranged in a desired pattern and spacing in order tocreate an electrode array. Individual wires within one or more electrodeleads connect with each electrode in the array. The electrode leads exitthe spinal column and may attach to one or more electrode leadextensions. The electrode lead extensions, or the leads, are typicallytunneled around the torso of the patient to a subcutaneous pocket wherethe IPG is implanted.

Spinal cord stimulators and other stimulation systems are known in theart. For example, an implantable electronic stimulator is disclosed inU.S. Pat. No. 3,646,940 issued Mar. 7, 1972 for “Implantable ElectronicStimulator Electrode and Method” that provides timed sequencedelectrical pulses to a plurality of electrodes. As another example, U.S.Pat. No. 3,724,467 issued Apr. 3, 1973 for “Electrode Implant For TheNeuro-Stimulation of The Spinal Cord,” teaches an electrode implant forthe neuro-stimulation of the spinal cord. A relatively thin and flexiblestrip of physiologically inert plastic is provided as a carrier on whicha plurality of electrodes are formed. The electrodes are connected byleads to an RF receiver, which is also implanted.

In U.S. Pat. No. 3,822,708, issued Jul. 9, 1974 for “Electrical SpinalCord Stimulating Device and Method for Management of Pain,” another typeof electrical spinal cord stimulation device is taught. The devicedisclosed in the '708 patent has five aligned electrodes which arepositioned longitudinally on the spinal cord. Electrical pulses appliedto the electrodes block perceived intractable pain, while allowingpassage of other sensations. A patient operated switch allows thepatient to adjust the stimulation parameters.

Most of the electrode arrays used with known SCS systems employ between4 and 16 electrodes. At least two electrodes are selectively programmedto act as anodes and cathodes, creating a bipolar stimulating group, orat least one electrode is selected to cooperate with the IPG case actingas a ground, creating a monopolar stimulation group. The number ofstimulation groups available, combined with the ability of integratedcircuits to generate a variety of complex stimulation pulses and pulsetrains, presents a multiplicity of candidate stimulation parameter setsto the clinician. When an SCS system is implanted, a fitting procedureis performed to select at least one stimulation parameter set for use bythe particular patient. The stimulation parameter set is selected forboth treatment efficacy, and to minimize power consumption. It isdesirable to try as many different stimulation parameter sets aspossible during a fitting session in order to increase the likelihood offinding a near optimal set.

A known fitting method is to manually test one parameter set, and thento manually deactivate the stimulation, select a new stimulationparameter set, and then to slowly increase the stimulation level from azero energy setting until the patient can perceive and assess the effectof the new stimulation parameter set. The testing of each stimulationparameter set is initiated at a zero energy setting. While this is arelatively safe procedure and avoids startling the patient duringfitting, it is a slow procedure which prevents large numbers ofcombinations of parameters from being tested in a reasonable period oftime. An alternative approach is to simply switch to a new stimulationparameter set at a stimulation energy setting similar to a levelpreviously exercised. However, even if the new stimulation parameter setprovides good results, switching parameter sets abruptly may provide anunpleasant sensation to the patient.

What is therefore needed is a system or method to quickly switch betweenstimulation parameter sets without causing uncomfortable sensations tothe patient.

SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing asystem or method for rapidly switching between stimulation parametersets of a Spinal Cord Stimulation (SCS) system, which system or methodincreases the number of stimulation parameter sets which may be testedduring a fitting procedure, or alternatively, reduces the time requiredfor the fitting procedure. The switching system or method comprises thefollowing steps, or means for achieving the following steps: selecting anew stimulation parameter set, setting the initial stimulation level ator below an estimated perception threshold of the patient for the newstimulation parameter set (the perception levels may be estimated basedon previous stimulation results), increasing the stimulation level todetermine a perceived optimal stimulation level, and/or a perceivedmaximum stimulation level (i.e., a discomfort level.)

In accordance with one aspect of the invention, there is provided asystem or method for rapidly measuring the effectiveness of a largenumber of stimulation parameter sets. Each new stimulation parameter setis initiated at a stimulation level at, or just below, the estimatedperception threshold for the stimulation parameter set, and thenincreased. As a result, the time required to increase (i.e, ramp up)from a zero energy setting, to the perception threshold, is eliminated.

It is a further feature of the invention to prevent discomfort resultingfrom initiating a new stimulation parameter set at a perceivablestimulation level. As a result of activating the new stimulation set ator below the perception threshold, the patient has no perception ofstimulation upon activation.

It is an additional feature of the invention to facilitate the selectionof a low energy level stimulation parameter set. The energy consumptionof an SCS system is an important system parameter because high energyconsumption may accelerate battery failure and create a requirement forbattery replacement. By allowing the comparison of more stimulationparameter sets, a lower energy level stimulation parameter set is morelikely to be tested and selected for inclusion in the SCS system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following more particulardescription thereof, presented in conjunction with the followingdrawings wherein:

FIG. 1 shows a typical Spinal Cord Stimulation (SCS) system;

FIG. 2 depicts the SCS system of FIG. 1 implanted in a spinal column;

FIG. 3A shows a pair of in-line electrodes used to provide twodimensional stimulation;

FIG. 3B shows a paddle-type electrode array used to provide twodimensional stimulation;

FIG. 4A shows an equipment suite suitable for an SCS trial phase;

FIG. 4B shows an equipment suite suitable for an SCS fitting phase;

FIG. 5 shows a prior art method of stimulation parameter set switching;

FIG. 6 shows a prior art method of stimulation Rarameter set switchingthat reduces time, but may produce undesirable side effects;

FIG. 7 shows a first embodiment of the present invention wherein thestimulation level is initiated below the perception level and thenincreased to a perceived optimal level;

FIG. 8 shows a second embodiment of the present invention wherein thestimulation level is initiated below the perception level and increasedto a perceived maximum level; and

FIG. 9 shows a flow chart of an embodiment of the method taught herein.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

Spinal Cord Stimulation (SCS) systems treat chronic pain by providingelectrical stimulation pulses through the electrodes of an electrodearray, which electrode array is placed epidurally next to a patient'sspinal cord. Elements comprising a typical SCS system 10 are shown inFIG. 1. An SCS system 10 typically comprises an Implantable PulseGenerator (IPG) 12, a lead extension 14, an electrode lead 16, and anelectrode array 18 residing on a distal end of the lead 16. The IPG 12generates stimulation pulses for implanted electrodes that make up theelectrode array 18. A proximal end of the lead extension 14 is removablyconnected to the IPG 12 and a distal end of the lead extension 14 isremovably connected to a proximal end of the electrode lead 16. Thein-series combination of the lead extension 14 and electrode lead 16,carry the stimulation pulses from the IPG 12 to the electrode array 18.

The SCS system 10 described in FIG. 1 above is depicted implanted in aspinal column 22 in FIG. 2. The electrode array 18 is implanted at thesite of nerves that are the target of stimulation, e.g., along thespinal cord. Due to the lack of space near the location where theelectrode lead 16 exits the spinal column 22, the IPG 12 is generallyimplanted in the abdomen or above the buttocks. The lead extension 14facilitates locating the IPG 12 away from the electrode lead exit point.

FIGS. 1 and 2 depict a typical SCS system, and other stimulation systemsmay utilize different components, utilize similar components organizeddifferently, or be implanted differently. The present invention may beexercised with any stimulation system utilized to treat perceived pain,which system utilizes a fitting procedure to adjust the stimulationparameters to a patient. Therefore, the application of the presentinvention to any stimulation system is intended to come within the scopeof the present invention.

An SCS system 10 may use a single in-line electrode array (onedimensional) or may use two or more in-line arrays 20 to create a twodimensional array of electrodes 22 as shown in FIG. 3A. An SCS system 10may also use one or more paddle arrays 24 with two or more columns ofelectrodes 26 to create a two dimensional array as shown in FIG. 3B.Multiple in-line arrays 20 or a paddle array 24 may be connected to anIPG 12 as shown in FIG. 1.

The SCS system 10 is entirely implanted in a patient 28 in normal use,but may be connected to a programming computer 30 during fitting. Afitting suite used during initial implantation is shown in FIG. 4A.During the initial implantation an External Trial Stimulator (ETS) 32 iselectrically connected by a transcutaneous cable 34 to the electrodelead 16. A second cable 36 connects the ETS 32 to the programmingcomputer 30.

A second fitting suite shown in FIG. 4B is used following implantationof the IPG 12. The second suite includes a hand held programmer (orpatient programmer) 38 which wirelessly communicates through the skinwith the IPG 12. The programmer 38 also communicates with theprogramming computer 30 using a third cable 40, an RF link, an IR link,or some other communications technique.

The method of the present invention may be exercised in the context ofthe first fitting suite, the second fitting suite, or any other systemadaptable to the fitting procedure. The exercise of the presentinvention with any fitting procedure using any equipment is intended tocome within the scope of the present invention.

A plot of stimulation level (i.e., energy setting) trajectories for afirst known (i.e., prior art) method of measuring the effectiveness of amultiplicity of stimulation parameter sets is depicted in FIG. 5. Eachstimulation parameter set comprises a unique combination of electrodes,electrode polarity, relative amplitude, pulse width, and pulse rate. Theperception threshold (the stimulation level where the patient starts tofeel the effect of the stimulation) is plotted as a solid dot, theoptimal stimulation level is plotted as a circle, and the discomfortthreshold (the stimulation level where the stimulation itself results indiscomfort apart from the pain being treated) is plotted as an “X”. Thevertical axis is the stimulation level, and the horizontal axiscorresponds to different candidate stimulation parameter sets. Thestimulation levels are initiated at zero and increased slowly to theperception threshold (i.e., where the patient first feels thestimulation), and on to the optimum stimulation level (i.e., where thepatient feels that optimal stimulation has been reached.) Additionally(not shown in FIG. 5), the stimulation level may be further increased todetermine the discomfort threshold. As is evident from FIG. 5, the firstknown method wastes a significant amount of time reaching the perceptionthreshold.

A plot of a second known (i.e., prior art) method is depicted in FIG. 6.The method of FIG. 6 activates stimulation at an estimate (plotted as an“e”) of the optimal stimulation level. The patient or clinician may varythe stimulation level about the estimated optimal level, and locate anoptimal level as perceived by the patient. This method eliminates thetime spent between the zero stimulation level and the perceptionthreshold, but has a drawback in that initiating the stimulation at aperceivable level of stimulation may cause an unpleasant sensation. Suchunpleasant sensation may prejudice the patient against the presentstimulation parameter set and against future parameter set switching,and thereby bias the overall results.

A plot of stimulation levels resulting from exercise of a first methodof the present invention is depicted in FIG. 7. The first method reducesthe time required by known methods to converge to an optimal stimulationlevel by activating stimulation at a stimulation level at or just belowan estimated perception threshold for the stimulation parameter setbeing tested (i.e., for a trial stimulation parameter set). The trialstimulation parameter set is selected from a set of candidatestimulation parameter sets comprising all of the stimulation parametersets being considered for the patient. The trial stimulation parameterset is generally an untested candidate stimulation parameter set. Afterinitiating stimulation, the stimulation level is then increased as shownin FIG. 7, and the patient indicates, for example, when a perceivedoptimal stimulation level is reached, thereby providing a measurement ofthe optimal stimulation level for the trial stimulation parameter set.The stimulation level may also be varied around the optimal stimulationlevel to ensure that the level first identified by the patient is trulythe optimal level. The patient may also indicate when the perceptionthreshold is reached, and/or when the discomfort threshold is reached.

After the optimal stimulation levels have been measured for all of thecandidate stimulation parameter sets, the stimulation may be switchedbetween two or more candidate stimulation parameter sets to determinewhich set provides the best results. In these cases, stimulation may beactivated at or just below the stimulation threshold, and then thestimulation level may be increased manually or automatically to theoptimal stimulation level measured previously for the candidatestimulation parameter set being exercised.

Because energy consumption is an important parameter of an implantablestimulation system, the energy consumptions of the candidate stimulationparameter sets may be recorded at the minimum effective stimulationlevel and/or optimal stimulation level of each candidate stimulationparameter set. Following the testing of all of the candidate stimulationparameter sets, a candidate stimulation parameter set providingeffective stimulation with a low energy consumption may be selected asthe stimulation parameter set to be used by the patient. Alternatively,one of a plurality of candidate stimulation parameter sets providingsimilar optimal stimulation results may be selected based on the energyconsumption required for optimal stimulation.

A method for obtaining estimates of the perception thresholds bymeasuring a subset of perception thresholds, and then estimating (e.g.,by interpolating) the perception thresholds for each untestedstimulation parameter set, is described in U.S. Pat. No. 6,393,325issued May 21, 2002 for “Directional Programming for ImplantableElectrode Arrays.” The '325 patent is incorporated herein by reference.

A plot of stimulation levels resulting from exercise of a secondembodiment of the present invention, wherein the discomfort threshold isbeing investigated, the stimulation level trajectories are as shown inFIG. 8. Stimulation is activated at or just below the perceptionthreshold, as in FIG. 7, but instead of only searching for the optimalstimulation level, the stimulation level is increased until the patientindicates that the stimulation is resulting in discomfort independent ofthe pain being treated.

In the embodiments described in FIGS. 7 and 8, the methods may bemodified by varying the stimulation level around the optimal stimulationlevel, and/or the discomfort threshold, to fine tune the measurement ofthe optimal stimulation level, and/or the discomfort threshold. Thepatient may directly vary the stimulation level, or a clinician may varythe stimulation level based on observations by the patient. Further, asthe perception thresholds for additional stimulation parameter sets aremeasured, the methods of the '325 patent may be reapplied to refine theestimated perception thresholds for stimulation parameter sets yet to betested.

A method for carrying out the present invention is depicted in FIG. 9and may be described as including the following steps:

-   -   Testing a subset of candidate stimulation parameter sets;    -   Collecting perception level data for the tested candidate        stimulation parameter sets;    -   Using the perception level data collected to estimate the        perception level for the untested candidate stimulation        parameter sets;    -   Selecting a trial stimulation parameter set from the untested        stimulation parameter set;    -   Providing stimulation using the trial stimulation parameter set        using the estimated perception threshold as the initial        stimulation level;    -   Increasing the stimulation level;    -   Measuring the perception threshold, and/or the optimal        stimulation level, and/or the discomfort threshold, and/or the        energy consumption at the optimal stimulation level for the        trial stimulation parameter set;    -   Selecting an untested candidate stimulation parameter set as a        new trial stimulation parameter set, and repeating the above;        and    -   After all of the candidate stimulation parameter sets have been        tested, selecting the best candidate stimulation parameter set.

The method described in FIG. 9 may further include the following:Varying the stimulation level to refine the perception threshold, and/orthe optimal stimulation level, and/or the discomfort level;

-   -   Recording the perception threshold, and/or the optimal        stimulation level, and/or the discomfort level, and/or the        energy consumption at the optimal stimulation level; or Holding        the stimulation level at a fixed stimulation level to        characterize the effect of stimulation at the fixed stimulation        level for a short period of time.

The basis for selecting the best candidate stimulation parameter set maybe one of the measured parameters, or a combination of the measuredstimulation parameters. Also, more than one candidate stimulationparameter set may be selected, wherein the patient may control which oneof a set of stimulation parameter sets is executed at any given time.

Those skilled in the art will recognize that other applications ofstimulation will benefit from the present invention, (e.g., stimulationto relieve migraine headaches, or peripheral nerve stimulation) and theuse of the present invention with those other applications is intendedto come within the scope of the present invention. Further, the presentinvention applies to measuring the effectiveness of any of thestimulation parameters, where activation above the perception thresholdmay cause unpleasant sensations, and is not intended to be limited tothe variation of any specific parameter.

As described above, the present invention allows rapid manual orautomatic switching between stimulation parameter sets, while avoidingunpleasant side effects that may result from activating stimulation at aperceivable stimulation level. The method applies to measurement of theminimum stimulation level required for effective stimulation, theoptimal stimulation level, and the discomfort threshold for astimulation parameter set. Further, the method may be applied tocomparing the effectiveness of several stimulation parameter sets. Astimulation system, and in particular an SCS system 10, may thus includeat least one stimulation parameter set selected from a multiplicity ofcandidate stimulation sets, wherein the stimulation system providesstimulation based on efficiently comparing the performance of all of themultiplicity of stimulation parameter sets.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A programmer for an electrode array configured for receivingstimulation pulses from an implantable pulse generator, the programmerconfigured for: selecting a new stimulation parameter set with a newcombination of electrodes or electrode polarity; selecting an initialstimulation level for the new stimulation parameter set, wherein theinitial stimulation level is selected to be a non-zero value not toexceed an estimated perception threshold of a patient for the newstimulation parameter set; generating initial stimulation commands basedon the new stimulation parameter set and the selected initialstimulation level; generating new stimulation commands based on the newstimulation parameter set and an increased stimulation level; andproviding the initial stimulation commands and the new stimulationcommands to the pulse generator.
 2. The programmer of claim 1, furtherconfigured for estimating the perception threshold of the patient. 3.The programmer of claim 2, further configured for estimating theperception threshold of the patient based on a previously recordedeffect of stimulation pulses on the patient.
 4. The programmer of claim1, wherein the non-zero value is a value at or just below the estimatedperception threshold of the patient for the new stimulation parameterset.
 5. The programmer of claim 1, wherein the new combination ofelectrodes or electrode polarity comprises a new subset of electrodes.6. The programmer of claim 1, further configured for recording theeffect of the stimulation pulses on the patient.
 7. The programmer ofclaim 6, further configured for recording the effect of the stimulationpulses on the patient by recording a perception threshold for the newstimulation parameter set.
 8. The programmer of claim 6, furtherconfigured for recording the effect of the stimulation pulses on thepatient by recording an optimal stimulation level for the newstimulation parameter set.
 9. The programmer of claim 6, furtherconfigured for recording the effect of the stimulation pulses on thepatient by recording a discomfort threshold for the new stimulationparameter set.
 10. The programmer of claim 6, further configured forrecording the effect of the stimulation pulses on the patient bymeasuring an energy consumption required for effective stimulation forthe new stimulation parameter set.
 11. The programmer of claim 6,further configured for recording the effect of the stimulation pulses onthe patient by: measuring at least one of a set consisting of aperception threshold, an optimal stimulation level, a discomfortthreshold, and an energy consumption required for effective stimulation;and varying the stimulation level around an initial measurement toimprove the measurement.
 12. The programmer of claim 1, furtherconfigured for holding the stimulation level at a fixed stimulationlevel to characterize the effect of stimulation pulses on the patient atthe fixed stimulation level for a short period of time.
 13. Theprogrammer of claim 1, further configured for: selecting a second newstimulation parameter set; selecting an initial stimulation lead levelfor the second new stimulation parameter set, wherein the initialstimulation level is selected so as to be a non-zero value not to exceedan estimated perception threshold of the patient for the second newstimulation parameter set; generating initial stimulation commands basedon the second new stimulation parameter set and the selected initialstimulation level; generating second new stimulation commands based onthe second new stimulation parameter set and an increased stimulationlevel; and providing the second new stimulation commands to the pulsegenerator.
 14. The programmer of claim 1, further configured for:collecting perception level data for a subset of a multiplicity ofstimulation parameter sets; and using the collected perception leveldata to estimate the perception level for untested stimulation parametersets.
 15. A programmer for an electrode array configured for receivingstimulation pulses from an implantable pulse generator, the programmerconfigured for: selecting a trial stimulation parameter set with a newcombination of electrodes or electrode polarity from a group ofcandidate stimulation parameter sets; selecting an initial stimulationlevel for the trial stimulation parameter set, wherein the initialstimulation level is selected to be a non-zero value not to exceed anestimated perception threshold of a patient for the trial stimulationparameter set; generating initial stimulation commands based on the newstimulation parameter set and the selected initial stimulation level;generating new stimulation commands based on the new stimulationparameter set and an increased stimulation level; providing the initialstimulation commands and the new stimulation commands to the pulsegenerator; and measuring the effectiveness of the stimulation pulses onthe patient; and selecting the preferred stimulation parameter set basedon measured effectiveness.
 16. The programmer of claim 15, furtherconfigured for estimating the perception threshold of the patient. 17.The programmer of claim 15, further configured for measuring theeffectiveness of the stimulation parameter set comprises recordingobservations made by the patient on the effect of the stimulationpulses.
 18. The programmer of claim 15, further configured for measuringthe effectiveness of the stimulation parameter set by measuring at leastone of a set consisting of a perception level, an optimal stimulationlevel, a discomfort threshold, and an energy consumption required foreffective stimulation, wherein the measuring is based on observationsmade by the patient on the effect of the stimulation pulses.
 19. Theprogrammer of claim 15, further configured for selecting the stimulationparameter set with the preferred effectiveness by retesting at least twopreviously tested stimulation parameter sets to compare theeffectiveness of each of the at least two previously tested stimulationparameter sets to the effectiveness of others of the at least twopreviously tested stimulation parameter sets, wherein each stimulationparameter set is initiated at a stimulation level selected to be anon-zero value not to exceed the perception threshold of the patient,and then the stimulation level is increased to a level the comparison isto be made at.
 20. The programmer of claim 15, further configured for,after measuring the effectiveness of the stimulation parameter set,using the measurement of the perception threshold obtained for thetested stimulation parameter set to improve the estimated perceptionthreshold for untested stimulation parameter sets.